High frequency oscillator and modulator



March 28, 1939. N. E. LlNDENBLAD HIGH FREQUENCY OSCILLATOR AND MODULATORFiled Novf24, 1954 INVENTOR N\ LS E. LINDENBLAD /fig ATTORNEY PatentedMar. 28, 1939 I a UNITED STATES PATENT OFFICE HIGH FREQUENCY OSCILLATORAND MODULATOR Nils E. Lindenblad, Port Jefferson, N. Y., assignor toRadio Corporation of America, a corporation of Delaware ApplicationNovember 24, 1934, Serial No. 754,559

' 6 Claims. (01. 179 17.1)

This invention relates to oscillation generators and an auxiliary grid5. Envelope l is provided and more particularly to a method of andapwith four stems or presses 6, 1, 8, 9. each indiparatus for generatingultra high frequency osvidual to an electrode so as to preventundesirable cillations. capacitive reactions between electrodes. For

Observations have shown that in using electron reasons which appearlater, auxiliary grid is 5 discharge devices in the generation of ultrahigh arranged to be a closer mesh and screen aifair frequencies, thecapacitive reactions at these than the main grid which is herein shownto be a frequencies reach such low values as to prohibit athe Open m s Suc u e The plate 4 is any appreciable voltage swings of the tubeeleshown to be of solid material throughout, but it 10 ments. Theelements will, in other words reis to be understood that since thebombardment 10 main rather inert and thus assert very little or of thiselectrode fr m the lectron i ve y sl h no control on the electrons,electro-dynamically if any at all, the Structure a e ma e of somespeaking, unless abnormal oscillating currents ht Screen material.

are used, which inherently is prevented by power F01 producing Oscilatio s t s p e er ed that limitations. This will be especially true forfrethe auxiliary grid 5 be maintained at a S t y 1 quencies above500,000 kc.- In the region between e e p t n t main d 3 at a high posi-0 and 500,000 kc., it has been found possitive potential and plate 4 ata somewhat negative ble to help the conditions, in otherwise somewhatpotential, all r l t v to the Cathode 2 W ch s unsuitable tubes, byspecial tuning arrangements. at neutral or ground potential.

One of the objects of the present invention is The theory underly tproduction of OS- 20 to provide an improved oscillation generator forcillations will now be iven. It is to be underthese short waves, andthis is achieved, genstood, however, that this theoretical explanationerally speaking, by making groups of electrons act s Ve mainly for t1011110086 0f p s on, and in such a way as to control their own flow andin der that t invention ay be tt anpulsations, electrodynamically moreindependent p e e While this theoretical explanetifln 2 5 of theelectrodes of the electron discharge devices; is believed to be correct,it is not of necessity comthe function of the electrodes then being onlyto p ete, 10 do the Operation 0f the invention d produce the electronemission condition required pend upon its accuracy or otherwise. by thephenomena and to furnish momentum to Due to the high positive potentialon the main the electrons. grid 3, electrons will be drawn from thecathode 30 A specific object of the present invention is to 2 towardgrid 3 in spite of the slightly negative provide an improved form ofbraking field or potential on the auxiliary grid 5. As theseBarkhausen-Kurz oscillator of the type wherein electrons travel towardthe main grid 3, they will a grid is maintained at a higher positivepotential be accelerated, and a number of them will strike relative tothe other electrodes of the oscillator, grid 3 and cause considerableheating of this 35 and wherein electrons have a pendulum or togrid. Itis believed that the electrons which and-fro motion about the grid.strike the main grid detach other electrons from A feature of theinvention lies in the provision this grid, possibly influencing them tofollow the of an auxiliary grid in the electron discharge deremainingcourse of electrons which pass through vice between the regular gridandthe cathode. the mesh of the main grid, thus adding secondary 40Other objects, features and advantages will apemission effect to thebraking field or Barkpear in the subsequent detailed description whichhausen-Kurz phenomena. The group of elecis accompanied by a drawingillustrating, diatrons which is mostly effective in causingoscillagrammatically, the improved oscillator of the tion generation,however, is the one that does not invention in connection with acomplete transland on the main grid 3 but passes through it. 45'

mitting circuit, given by way of illustration only. Immediately uponpassing through the main grid Although the oscillator oi the inventionis here- 3, the velocity of the electron group will be rein shown in atransmitting circuit, it will be tarded, inasmuch as the high positivemain grid understood, of course, that it is not limited thereis nowbehind the negative electrons instead of so to, sinceit may just as wellbe used in a receiving ahead of them. If the potential of the plate 4 iscircuit. zero, the electrons will then have lost all their The drawingillustratesa cross sectional View of velocity upon arriving at theplate. Some of the oscillating electron discharge device compristheseelectrons may land on the plate and will ing an evacuated envelope I,enclosing an electhen produce a direct current component in its tronemitting cathode 2, a plate 4, a main grid 3 circuit. The electronsstopping in front of the 5s plate have the effect of repelling laterarriving electrons sooner, while the latter cause the early electrons tobe held over. The result is that the electrons turn around more nearlyat the same time for their return travel, and thus organize themselvesinto a group. From the foregoing it will be evident that it is,desirable to give the plate a somewhat negative potential, in which casethe electrons will stop in space at such a point where the gradientbetween the positive main grid 3 and the negative plate 4 reaches zero.As soon as a negative layer of electrons is formed in this space, itsnegative potential will add to that of the plate and result in movingthe zero point of the space voltage gradient farther towards the maingrid.

In considering the phenomena occurring at the plate, it is found that,actually, there is a slight flow of current even when the plate ismaintained at a negative potential, since some of the early arrivingelectrons are pushed into the plate by later arriving electrons. It mustalso be remembered that, due to the temperature of the cathode, theelectrons will have a certain velocity given to them which is not due tospace gradient. This initial momentum may make the electrons travelbeyond the zone set by the zero of the voltage gradient and cause themeventually to reach the plate 4. The secondary emission from the hotmain grid 3 may further add indirectly to this phenomena; thus electronsmay be brought all the way to the surface of the plate in spite of itsbeing at a negative potential. Irrespective of what takes place near theplate, a very small change in potential on the plate will decide whetherelectrons are to be drawn towards it or repelled from it. In thisconnection, the. tuning of the plate aids in determining this condition.

As for the returning electrons on their journey back towards the maingrid 3, it is believed that many of these electrons land on the wires ofthe grid, the remaining ones continuing towards the cathode under theretarding force exerted by the main grid. Since a considerable portionof the electrons originated at the cathode, they possess sufficientmomentum to carry them back towards the vicinity of the cathode. Theywill, however, fall short of reaching the cathode since during theirtravel they have induced currents in the external circuit. The electronshave, therefore, given up some of their kinetic energy. Theiroscillation is alternated, and their amplitude about the grid becomessmaller and smaller until they are finally lost in the grid. Of courseonly very few electrons live through a completely attenuated oscillationlife. Most of them are lost on the grid during their early cycles. Thegroup, as a whole, is not attenuated, since lost electrons arecontinually renewed. The group amplitude of oscillation assumes anaverage value of the individual electron oscillation amplitude. It canthus be seen that the group does not reach the cathode but forms anegative space charge at its turning point in front of the cathode,similar to the phenomenon in front of the plate, and thus reduces theemission from the cathode towards the main grid. The returning electronsreduce the emission to the main grid until they are themselves drawntowards that grid and repeat the procedure or cycle over again. Thespace charge around the cathode will then clear out at least partiallyand more emission will again be possible. This pulsation in the emissionis helpful in further organizing the electrons into a group so thatstray oscillations obtain in the external circuit. It will thus be seenthat the period of this type of oscillation is Wholly independent of anytuning phenomena, but depends solely on the space gradients and emissiondensities, although it is known that mixed phenomenas do occur and thatthe operation may be explained in a number of ways.

It will now be seen that the auxiliary grid 5 offers a means by whichthe space charge around the cathode may be controlled. Although theprimary function of auxiliary grid 5 is to provide a condition underwhich the returning electrons may more completely shut ofi the emissionfrom the cathode to the main grid and thus allow an increase in poweroutput from the electron discharge device, still if the auxiliary gridis made to have a slightly negative variable potential the path of theelectrons emitted from the cathode to the main grid may be so regulatedthat the electrons pass through a very narrow space in the center of theopenings between each wire in the auxiliary grid. The returningelectrons will also select this same center for their return passagetowards the cathode as the centers have minimum negative potential. thenarrow passageway will offer considerable stagnation and possiblycomplete shutoff of outgoing electrons from the cathode, whichcondition, if obtained, produces efiicient power output from theelectron discharge device.

For tuning the oscillator there are provided parallel tuned circuits Illand H in the auxiliary grid and plate circuits respectively. Anysuitable utilization circuit, such as an antenna I2, is shownelectromagnetically coupled to the tuned plate circuit H through atransmission line It. Potentiometers l6 and I! enable variation of thevoltages applied to auxiliary grid 5 and plate 4, respectively. Aconnection l8 extends between the potentiometer l1 and the main grid 3.The I-Ieising method of modulation is herein shown for modulating theoscillations, a modulation input circuit H, which may be a telegraphkey, or a speech circuit, being coupled to a vacuum tube I5 whose outputis connected to the main grid 3 of the oscillator tube.

It will be understood that the structure set forth in the drawing isentirely illustrative and not definitive, since various changes may bemade in the form, shape, and arrangement of the various elements andcircuits without departing from the spirit and scope of the invention.

What is claimed is:

1. An oscillation generator comprising an electron discharge devicehaving within its envelope a cathode, a plate, a grid between saidcathode and plate, and an auxiliary grid between said cathode and firstgrid, and means for maintaining said first grid at a high positivepotential and said auxiliary grid and plate at a slightly negativepotential relative to said cathode, both said first grid and saidauxiliary grid comprising screens, the screen of said auxiliary gridhaving a closer mesh than the screen of said first grid.

2. In combination, an oscillation generator of the braking field typecomprising an electron discharge device having within its envelope acathode, a plate, a grid between said cathode and plate, and anauxiliary grid between said cathode and first grid, a source ofpotential for maintaining said auxiliary grid at a slightly negativepotential relative to said cathode, a parallel tuned circuit connectedbetween said first grid and cathode, a connection including a paralleltuned circuit between said source and said aux- In this manner iliarygrid, means for maintaining said first grid at a high positive potentialrelative to said cathode, means for maintaining said plate at a muchless potential than said first grid, and a parallel tuned output circuitcoupled between said plate and cathode, said auxiliary grid beingconstituted by wires which are more closely spaced than the wires ofsaid first grid, whereby substantially complete electron cut-01f fromsaid cathode to said first grid can be effected.

3. In combination, an oscillation generator of the braking field typecomprising an electron discharge device having within its envelope acathode, a plate, a grid between said cathode and plate, and anauxiliary grid between said cathode and first grid, a source ofpotential for maintaining said auxiliary grid at a slightly negativepotential relative to said cathode, a parallel tuned circuit connectedbetween said first grid and cathode, a connection including a paralleltuned circuit between said source and said auxiliary grid, means formaintaining said first grid at a high positive potential relative tosaid cathode, means for maintaining said plate at a much less potentialthan said first grid, a parallel tuned output circuit coupled to saidplate, and means coupled to said first grid for modulating theoscillations produced, said auxiliary grid being constituted by wireswhich are more closely spaced than the wires of said first grid, wherebysubstantially complete electron cut-01f from said cathode to said firstgrid can be efiected.

4. In combination, an oscillation generator of the braking field typecomprising an electron discharge device having within its envelope acathode, a plate, a grid between said cathode and plate, and anauxiliary grid between said cathode and first grid, a source ofpotential for maintaining said auxiliary grid at a slightly negativepotential relative to said cathode, a tuned circuit connected betweensaid first grid and cathode, a

connection including a tuned circuit between said source and saidauxiliary grid, means for maintaining said first grid at a high positivepotential relative to said cathode, a conductive connection comprising aresistance connected between said first grid and said cathode, means formaintaining said plate at a much less potential than said first grid, aparallel tuned output circuit coupled to said plate, a connection from apoint intermediate the ends of said resistance to the means formaintaining said plate at a desired potential, and means coupled to saidfirst grid for amplitude modulating the oscillations produced.

5. In combination, an oscillation generator of the braking field typecomprising an electron discharge device having within its envelope acathode, a plate, a grid between said cathode and plate, and anauxiliary grid between said cathode and first grid, a source ofpotential for maintaining said auxiliary grid at a slightly negativepotential relative to said cathode, a parallel tuned circuit connectedbetween said first grid and cathode, a connection including a paralleltuned circuit between said source and said aux iliary grid, means formaintaining said first grid at a high positive potential relative tosaid cathode, and means for maintaining said plate at a much lesspotential than said first grid, said auxiliary grid being constituted bywires which are more closely spaced than the wires of said first grid,whereby substantially complete electron cut-off from said cathode tosaid first grid can be efiected.

6. A generator in accordance with claim 1, inl cluding a resistanceconnected between said first grid and cathode, and a conductiveconnection from a point intermediate the ends of said resistance to saidplate.

NILS E. LINDENBLAD.

